The present invention relates to instruments for preparing a glenoid surface of a scapula to receive a prosthetic glenoid component to replace the natural socket of a shoulder. More particularly, the present invention relates to a drill guide assembly for aligning and guiding a drill bit to form holes in the glenoid surface at predetermined locations to receive attachment pegs formed on the glenoid component to secure the glenoid component to the glenoid surface. A reamer assembly including a ratchet drive mechanism is also included to facilitate preparation of the glenoid surface prior to installation of the glenoid component.
The instruments of the present invention are designed for use during a total shoulder replacement procedure. In a total shoulder replacement procedure, a humeral component having a head portion is used to replace the natural head portion of the arm bone or humerus. The humeral component typically has an elongated intramedullary stem to secure the humeral component to the humerus. The glenoid portion of the scapula is resurfaced with a glenoid component which provides a bearing surface for the head portion of the humeral component.
In order to install the glenoid component to the glenoid surface, it is necessary to drill holes in the glenoid surface for receiving attachment pegs formed on the glenoid component used to secure the glenoid component to the glenoid surface. It is known to use a drill guide to guide a drill bit to form holes in the glenoid surface at predetermined locations.
During the installation of glenoid components, it is often difficult to access the glenoid surface through the surgical incision. The precise angle at which the surgeon must approach the glenoid surface can vary with each operation. The surgeon typically has very little room to maneuver the instruments used to prepare the glenoid surface for receiving the glenoid component. Because installation of the glenoid component requires accurate positioning of the instruments on the glenoid surfaces, the limited access to the glenoid surface during the operation can cause problems.
Prior art drill guides include a rigidly attached handle aligned in only one orientation with respect to the drill guide Therefore, the glenoid surface can be approached from only one angle which is controlled by the angle that the handle is attached to the drill guide. Prior art drill guides require two separate drill guides having the handles mounted in different positions for use on the right and left side glenoid surfaces.
Prior art reamers are either hand held or designed to be attached to a drill for reaming the surface of a bone to prepare the surface for receiving prosthetic components. Because of the limited space available for accessing the glenoid surface, it is difficult to properly position a reamer on the glenoid surface to smooth and prepare the glenoid surface for receiving a glenoid component.
One object of the present invention is to provide a drill guide having an adjustable handle to facilitate positioning of the drill guide on the glenoid surface.
Another object of the present invention is to provide a ratchet mechanism for driving a reamer assembly to permit rotation of a reamer against the glenoid surface to prepare the glenoid surface for installation of a glenoid component despite the limited access available during a shoulder replacement procedure.
Yet another object of the present invention is to provide a mechanism for accurately aligning and guiding a drill bit to form a plurality of holes in a glenoid surface at predetermined locations for receiving a plurality of attachment pegs attached to a glenoid component to secure the glenoid component to the glenoid surface.
According to the present invention, an assembly is provided for aligning and guiding a drill bit to form a hole in a glenoid surface of a scapula at a predetermined location. The assembly includes a drill guide having a first surface for abutting the glenoid surface and an opposite outwardly facing second surface. The drill guide is formed to include an aperture extending between the first and second surfaces for guiding the drill bit to form a center hole in the glenoid surface. The assembly includes a handle for positioning the drill guide on the glenoid surface to align the aperture at the predetermined location over the glenoid surface. The assembly also includes means for coupling the handle to the drill guide in a selected one of the plurality of orientations to align the handle at a selected angle with respect to the drill guide to facilitate positioning of the drill guide on the glenoid surface.
In a preferred embodiment of the present invention, the drill guide includes a projection extending outwardly from the second surface. The coupling means includes a head portion attached to the handle for engaging the projection to align the handle in the selected orientation with respect to the drill guide.
In another preferred embodiment of the present invention, the drill guide includes alignment means coupled to the drill guide for engaging a portion of the glenoid to align the drill guide aperture in its predetermined location over the glenoid surface. The alignment means includes an L-shaped armed having a first leg coupled to the drill guide and a second leg for engaging the glenoid to align the drill guide aperture in its predetermined location and to stabilize the drill guide while drilling the hole.
In yet another preferred embodiment of the present invention, the drill guide includes a plurality of apertures for guiding the drill bit to form a plurality of holes in the glenoid surface in various positions relative to the center hole. An alignment peg may be included on the drill guide for insertion into the center hole formed in the glenoid surface to position the plurality of drill guide apertures at predetermined locations in relation to the center hole.
The glenoid component installation instruments of the present invention also include an assembly for reaming the glenoid surface of the scapula to prepare the glenoid surface for receiving the glenoid component. The assembly includes a reamer having a cutting face which is rotatable about an axis of rotation. The cutting face is designed to be rotated in only one predetermined direction for smoothing and preparing the glenoid surface. The reamer assembly also includes ratchet means coupled to the reamer for intermittently rotating the reamer in a predetermined direction about the axis of rotation. The reamer assembly further includes means rotatably coupled to the ratchet means for receiving a pressure force along the axis of rotation to cause the cutting face of the reamer to engage the glenoid surface.
In still another preferred embodiment of the invention, the ratchet means includes a drive member coupled to the reamer for rotating the reamer about its axis of rotation in the predetermined direction and an oscillating member coupled to the drive member for providing intermittent rotational movement to the drive member. The oscillating member includes a handle for alternately rotating the oscillating member in the first predetermined direction and in a second direction opposite the first direction. The handle is aligned at a predetermined angle with respect to the axis rotation.
One feature of the present invention is the provision of a drill guide having a detachable handle and means for coupling the handle to the drill guide in a selected one of a plurality of orientations to align the handle at a selected angle with respect to the drill guide. Advantageously, this feature permits a surgeon to select an angle for attaching the handle which makes positioning the drill guide on the glenoid surface as easy as possible. In addition, the adjustable handle permits a single drill guide to be used for drilling both the left and right side glenoid surfaces. Therefore, the present invention facilitates the formation of holes in the glenoid surface for receiving attachment pegs to secure a glenoid component to the glenoid surface.
Another feature of the present invention is the provision of a reamer assembly including a ratchet drive mechanism for rotating a reamer about its axis of rotation to prepare a surface of a bone for receiving a prosthetic component. Advantageously, the ratchet assembly permits rotation of the reamer against the bone surface despite the limited access available during the normal surgical procedure. The ratchet drive mechanism causes rotation of the reamer in a single direction upon oscillating movement of an oscillating member of the ratchet assembly.
Additional objects, features, and advantageous of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.